29 March 2010

While my original idea in making up the bike electro-mechanic odometer described in the last past was to get rid of batteries on a bike, a friend told me that for ordinary people getting rid of the spoke sensor of the classical odometer is a much better selling point for the hub-dynamo driven odometer. Batteries in bike odometers usually last several years, so there is little pragmatic need to rid of them. I also agree with him that most people will probably prefer a digital odometer (much resembling the ones on the market now) to a mechanical one. While I still think that an electro-mechanic odometer would be a nice luxury bike component (just like Swiss mechanical watches are still a popular accessory among the rich elite), a more traditional digital odometer would be much easier (and cheaper) to make and could offer the features at the same price as state-of-the-art current odometer – just that it dispenses with the spoke-sensor and batteries.

My friend and I have come up with two ways to make a sensor-less and battery-less odometer: first is to use off-the-shelf generic components like a dot-matrix LCD and micro-controller – this allows us to build an experimental prototype at low cost as well as some practical devices for our own bike at an affordable price. We agreed to build this together just for fun!

If we ever were to commercialize it, however, we would need to drop to price to the same €20 range as current commercial models which requires custom-made components that are mass-produced with high initial investment cost. Personally I think there could be a middle way by re-using the shell and LCD of a cheap generic odometer and just replace the electronics with ours. In Europe (at least Denmark, Netherlands, Germany, Austria, and Switzerland) hub dynamos are now common place on utilitarian and travel bicycles and even on some sport bicycles. (That's because dynamo-lights are legally mandated for bikes used in public traffic and hub dynamos have replaced all other dynamos on new bikes.) Therefore the market for a spoke-sensor-free and battery-free bike odometer is huge. There are currently ca. 5 million new bikes sold in Germany each year and the amount is probably the same in the sum of the other four countries mentioned. If half of those bikes has a hub dynamo then that's 5 million potential odometer-buyers each year just in those five countries!

21 March 2010

Knowing how far you've gone is very useful when cycling. It can help you find your way with the help of a map (for ex. to “turn right after 1.5 km”), find which of a set of alternative routes is shorter, know how much workout you had, and estimate how far you still have to go on your trip. A classical odometer offers two counters, one resettable “trip” counter and one non-resettable “lifetime” counter, both having their own scale. The odometer proposed here shows just those two counters in the form of black digits printed on a white background, the digits sliding behind a little window. This has the advantage of being very readable, high-contrast, good-looking, robust and not using any power to display the numbers. The counting up is done using impulses from the bicycles hub dynamo and uses almost no power from the wheels. Resetting the trip counter is done mechanically with the user's gesture being the power-source. This construction ensures that the counter always displays the current mileage and is resettable even when the bike is not running or has not been running for a long time.

Here are some advantages of the proposed odometer:

high readability, always-on display

ease of use with only one dial (or button) to reset the counter

no parts attached to the bike wheels; only a small cable branching of the lighting system

no battery needed, therefore no need to swap batteries

very little energy use which does not noticeably increase the loss power of a normal hub dynamo

Here's a very sketchy drawing of how the odometer integrates with the handlebars. The top line shows XXX.X km and the bottom XX XX0 km.

And here some more detailed design information: the trip counter has four digits, the smallest counting 100 m. The life-time counter also has four digits with the smallest counting each 10 km. The longest trip will therefore be 999.9 km, which has been chosen because some people ride more than 100 km in a day and other might want to count trips of more than a day. The life-time counter will relapse to 0 after showing 99'990 km which is enough for most bicycles, although not enough for people who really ride a lot and keep the bike for more than a decade. (For an example see Rohloff Wanted day.) For those people there will be a luxury version of the counter with two times five digits: the trip counter measures each 10 m and the life-time counter goes up to 999'990 km. I would think that some people would buy this extended counter just to show off how far their bike is designed to go!

The two photos above show historic counters with little disks carrying the digits. To make the counter slimmer to integrate it better with the handlebars, the disks can be replaced by a little strip that turns around two pins as shown in the pseudo model on the right. Designing the electronics for this device will not be totally trivial because it has to deal with a wide variety of currents and voltages coming from the dynamo at different speeds and with lights on or off. There will several hidden digits to account for fractions of the distance displayed. Alternatively those values could be stored in some digital solid-state memory of a couple bits. In any case, storing this information won't use any power. The only power supply will be to increase the invisible counter which at every full interval will increase the visible counter. I wish I knew somebody who could figure those electronics out for me!

A variant with speedometer would use a classical needle to show the bike's current speed on a scale and it would additionally have a counter for the time of the current trip (accumulated time with speed >0). Then a second needle would show the average speed of the trip (which is the dividend of trip length and trip time so far). This second needle would be held in place with a gearing mechanism that doesn't need any power either. So when you stop the bike, the current speed will drop to 0 and stay there while the average will just stay where it was. When you sleep during a cold night that would drain any batteries and come back the next morning, the needle will still show your trip's average speed. I think that's reliability! And that's cool!